In a typical injection molding apparatus, a manifold having a manifold channel delivers melt to a plurality of hot runner nozzles. The hot runner nozzles are received in respective openings in a mold plate and extend between the manifold and a plurality of mold cavities. Each nozzle includes a nozzle channel that is aligned with an outlet of the manifold channel to receive melt therefrom and to deliver the melt to a mold gate of a mold cavity. The nozzles are coupled to an outlet surface of the manifold and a seal must be maintained therebetween in order to prevent leakage and allow for the injection molding apparatus to operate efficiently.
Typically, a collar is provided between the mold plate and a head of each nozzle to couple the nozzle to the outlet surface of the manifold. Since each collar must contact both the heated nozzle and the cold mold plate in order to align the nozzle with the manifold channel and the mold gate, a significant amount of heat may be lost from each nozzle. In an effort to reduce the heat loss often the collar includes a circular undercut that may be provided on one or both of the inner surface and the outer surface thereof. Typically, the area of the collar in contact with the nozzle remains relatively large in order to maintain the strength of the part to prevent failure under the lateral forces concentrated on the collar after thermal expansion of the system, those forces are large enough to maintain a sealing force between the nozzle and the manifold. The relatively large contact area of the collar concentrates the heat loss and results in a significant decrease in temperature in the contact area. Such heat loss is undesirable and may adversely affect the molding process resulting in poor quality molded parts being produced. It is therefore desirable to minimize the amount of heat that is lost from the nozzle through the collar.